1. Field of the Invention
The present invention relates generally to antenna structures coupled to electronic devices. More specifically, the present invention concerns extendable antennas for portable expansion cards.
2. The Prior State of the Art
Various communication systems are used to allow electronic devices, such as laptop computers, to communicate and exchange data and other types of information. For example, various networks, including Local Area Networks (LAN), Internet, Ethernet and conventional telephone networks, often link computers. These known communication systems, however, usually require the computer to be physically connected to telephone lines, modems or specialized wiring. In some locations, however, it is difficult if not impossible to be physically connected to the communication system. Additionally, these known systems generally cannot be used if the user is traveling or moving to different locations, as is typically the case with a laptop computer.
Wireless or cellular telephone systems enable portable expansion devices to connect laptop computers to a communication system. One such configuration is a cellular telephone system coupled to a portable expansion device, because the computer does not have to be connected to an existing telephone line. In addition, cellular telephone systems are very useful in connection with portable computers because the cellular communication circuitry can be miniaturized and provided as a component of the computer or placed on a portable expansion card.
Another particularly effective configuration allowing laptop computers to communicate is a Wireless LAN (WLAN) system. Some WLAN systems implement the IEEE 802.11 wireless standard, a protocol standard that resolves many interoperability issues among the manufacturers of WLAN equipment. The 802.11 standard requires both a medium access control (MAC) comprised of several functional blocks and a physical (PHY) control including diffused infrared, direct-sequence spread-spectrum (DSSS) and frequency-hopping spread spectrum (FHSS). Specifically, 802.11 supports DSSS for use with binary phase shift keying (BPSK) modulation at a 1-Mbit/second data rate (with higher data rates also deployed and developed) and quadrature phase shift keying (QPSK) modulation at a 2-Mbit/second data rate. The DSSS has an RF modulation bandwidth of 22 MHz (null to null). Both spread spectrum techniques are typically used in the 2.4-GHz band, because of its wide availability in many countries and the lower hardware costs as compared to higher microwave frequencies. WLAN systems and cellular telephone systems are both part of the latest technology craze attempting to integrate wireless communication onto portable electronic devices, and more specifically onto a portable expansion card. Portable expansion cards developed when the industry recognized that standardization of peripheral devices would, among other things, greatly increase the demand for them. Exemplary portable expansion cards include solid-state interface cards, PC Cards, ATA (Advanced Technology Attachment) cards, Compact Flash cards, SmartMedia cards, SSFDC (Solid State Floppy Disk Cards), or other miniature expansion card devices. Several manufacturers collaborated to form the Personal Computer Memory Card International Association (PCMCIA), which developed and promulgated standards for the physical design, dimensions, and electrical interface of portable expansion devices. Specifically, the PCMCIA PC Card standard identifies three primary card types: Type I, II, and III. These PC Card types correspond to physical dimension restrictions of 85.6 mm (length)×54.0 mm (width) and height restrictions of up to 3.3 mm: (Type I), 5.0 mm (Type II), and 10.5 mm (Type III). Now, many electronic devices being manufactured, especially those having a reduced size, are adapted to accommodate these standards. Laptop computers, in particular, are increasingly popular for both business and personal applications due in part to the development of PC Card peripheral devices designed to increase the functionality of the computers. As an example, PC cards are commonly used with portable and laptop computers to provide added features and/or functions. For instance, PC cards are often configured to function as memory cards, wireless network interface cards (NIC), sound cards, modems, or other devices that supply add-on functionality.
In the case of the wireless NIC, one of the greatest difficulties in moving the added wireless features to the PC Card is placement of all the necessary components on the PC Card. Specifically, the antenna structures presently used take up too much space within the PC Card housing and requires the short-range wireless stack, link manager, RF baseband, power amp, and other radio components to be placed on limited printed circuit board (PCB) space. In diversity radios, the PCB space shortage is further amplified by the need for multiple antenna structures and the related spatial separation requirements of the antenna structures. In fact many wireless NIC manufacturers are forced to extend the antenna structure past the PC Card specification via a fixed endcap structure. This permanent extension exposes the antenna structure to continual risk of damage as long as the PC Card is in the laptop computer expansion slot, whether or not the PC Card is active.
The WLAN and cellular telephone wireless systems previously mentioned often require specialized antennas, such as a diversity antenna structure used with the aforementioned diversity radio. Antenna structures, predominantly used for communication, efficiently transmit and receive electromagnetic energy in the form of radio waves. Antenna structures are used whenever it is impractical, or impossible to use a physical connection, such as a transmission line or wave-guide. In order to get the best performance out of the wireless antenna, the antenna must not be obstructed by anything within its path of radiation.
Antenna design attempts to achieve good impedance matching to the feeding transmission line to maximize the available power for radiation. Often the power levels are limited by transmission standards. For example “Bluetooth” wireless technology is a de facto standard, as well as a specification for small-form factor, low-cost, short-range radio links between laptops, phones, and other portable digital devices. One of the present Bluetooth specifications is to limit the transmission range to around 10 meters. Thus, while a Bluetooth antenna is designed to distribute the radiation optimally, it has a limited transmission range due to the wireless standard.
Antenna design also attempts to achieve the best compromise between the various constraints imposed on the desired radiation pattern. Optimization of the radiation pattern may include maximizing the radiation in one direction and suppressing it in others. If a specific desired radiation pattern is difficult or impossible to obtain using a single antenna, antenna engineers will often resort to designing arrays of simple antennas. Adjustment of the amplitude and phase of the feed voltages to the various elements in the array, as well as the geometrical arrangement of these elements, often achieves the desired radiation characteristics. Unfortunately, antenna array design is complicated by the mutual interaction between the various elements in the array and the operating environment of the array.
One example of a more difficult operating environment with multiple mutual interacting components that affect the desired radiation patterns is a laptop computer. Different brands of laptop computers use different shielding components for electromagnetic interference (EMI) that affect the antennas quite dramatically from one vendor to another. For example, some laptop computers use conductive materials or fillers, such as exotic conductive plastic material, that interfere with fully integrated antenna arrays in the PC Card housing. Of course, the laptop display screen also presents a difficult shielding problem of the radiation pattern depending on how the antenna is configured. Furthermore, a user is generally positioned in front of the laptop computer, thereby blocking a portion of the receiving area and obstructing the desired radiation pattern. Obstruction by the user is especially important with a low power wireless signal, where it is easy to block the signals and to absorb the radiation pattern.
To compensate for these difficulties many wireless NIC configurations utilize an external antenna structure that is selectively detachable from the portable expansion card and can be placed away from the laptop environment. Conventional external antenna structures used to connect a computer to a wireless communication system or cellular telephone are typically placed externally of the computer because of the noise, interference, obstruction and shielding caused by the various components of the computer. In particular, conventional antenna structures do not function correctly if they are obstructed or shielded by the housing or other structures of the computer.
Conventional antenna structures are also generally rigid and they protrude a relatively long distance from the body of the computer. These protruding antennas are often large, unwieldy, aesthetically unpleasing and they make the computer difficult to move and transport. In addition, these antennas are often bent, broken, knocked out of alignment or otherwise damaged because they can easily catch or strike foreign objects such as people, walls, doors, etc. Further, these known antennas require a large support structure to secure the antenna to the housing of the portable expansion device and this support structure requires a considerable amount of valuable space inside the body of the portable expansion device. Despite its size, the support structure is often damaged when the antenna is accidentally moved.
It is known that the repair and replacement of conventional antennas and the associated support structure is difficult and costly. In fact, the entire antenna assembly is often removed and replaced instead of attempting to repair a portion of the antenna or support structure. Thus, the repair and replacement of the antenna and/or antenna support structure is expensive and time consuming.
In order to alleviate these problems, known antennas are often removed before the computer is moved or transported. Additionally, known antennas must often be removed before the computer can be inserted into its carrying case. Disadvantageously, this requires additional time and resources to remove and reattach the antenna each time the computer is moved. Additionally, the antenna is often misplaced, lost or damaged when it is detached from the computer. Further, because the user often does not want to take the time and effort to remove the antenna, the computer is moved with the antenna still attached to the computer and this frequently results in the antenna being damaged or broken.
Additionally, it is well known that an antenna should usually be placed in a vertical position to obtain the optimum signal strength. This is because the antenna is most often located just above a conducting horizontal plane such as a metal desktop, which acts as a reflecting ground plane that attenuates horizontal components of the electromagnetic wave. Further, this and other conventional antennas have limited connectivity when the antenna extends in a horizontal plane and the housing of the computer may obstruct or shield the antenna. As such, most retractable antennas require additional adjustments once they are extracted, such as vertical repositioning via pivot points. These pivot points are also subject to failure overtime at a moving joint. The repair and replacement of these integrated antennas is difficult and costly. In fact, the entire attached PC Card assembly is often removed and replaced instead of attempting to repair a portion of the integrated antenna or support structure. Thus, repair or replacement of the integrated antenna in the PC Card is expensive and time consuming.
Presently, integrated retractable antenna diversity solutions are not found. Single antenna solutions do not have adequate radiation coverage considering the operating environment of most digital devices. A single antenna may also be partially blocked by the operator or an object that is between the antenna and its intended point of communication. Poor coverage, mechanical reliability, aesthetics, blockage of a single antenna due to an intervening object or multipath are all problems with these non-diversity solutions. Most attempted extendable antenna designs lack stability and robustness and force the design to go to a permanently extended solid endcap antenna structure.